Loved the grappling hook mechanic. It was a little hard to figure out what to do at first, but once I understood the control mechanics it was great. Nice feeling of floating through space. Great atmosphere. Fun game!
Edit.. took me two tries to get to the end. I quit early, because I thought I had seen it all, but I came back. Glad to find there's another "level" with a pretty distinct feeling from the open space portions.